text:
How does handover between Air Traffic Controllers work?
I have a questions about air traffic control.
I understand how the controllers monitor and direct aircraft on their intended routes while maintaining clearance distances to other aircraft and obviously recognizing and avoiding collision courses, or at least I think I do.
My question is about hand-offs and range.
Presumably traffic is handed over to the next area controller when it approaches or reaches the limit of the controllers radar scope. However, how can the controller know that there is not another aircraft approaching out of scope range that is on a collision course with the aircraft leaving or approaching or traversing the boundary of his scope range?
Wiki says...

As an aircraft reaches the boundary of a center's control area it is "handed off" or "handed over" to the next area control center. In some cases this "hand-off" process involves a transfer of identification and details between controllers so that air traffic control services can be provided in a seamless manner; in other cases local agreements may allow "silent handovers" such that the receiving center does not require any co-ordination if traffic is presented in an agreed manner. After the hand-off, the aircraft is given a frequency change and begins talking to the next controller. This process continues until the aircraft is handed off to a terminal controller ("approach").

From that I guess is some centres the controller is expecting an aircraft to appear from a particular bearing, though even then, the variance would be wide at radar ranges.
I also realize that aircraft normally follow set lanes and altitudes depending on direct etc, but an aircraft in transition could appear pretty much anywhere. No?
That got me thinking that there must be an overlap on the visible range and that an aircraft is, for some period of time, visible from both centers. I guess that would work, but then it got me wondering how each centre knows who has control over the aircraft and if situations could occur where nobody is...?
That all brought up another question. I have to assume there is more than one human at busier control centers all working together. How is that managed? Who controls what?

As someone with over 1000 rep surely you should know that asking so many questions in one post like this will likely have it closed as too broad. These could easily be asked as a series of smaller questions.

This site works best when you ask one question, and use the title to summarise that question. I've edited the title to a single question for you, but I think the body of your question is still really multiple separate questions.

Ya sorry about that, they kind of flow together as a whole though. Or I think they do.

@Notts90: It's obvious a single answer will cover all these details, I believe the OP is just ensuring the answer will be detailed enough.

@mins I disagree about it being obvious and also think some would be better and more useful as stand alone questions.

@SteliosAdamantidis I thought about that and decided to go with what seemed like the more likely search term, thinking that an answer would probably be general enough to cover an area control centre and an airport tower. I still think this is separate questions: one needing an answer about radar extending beyond airspace, one needing an answer about passing details between controllers in different places, and one needing an answer about how responsibilities are split at a single airport.

Sorry if it irritates some that I have so many parts to the question. But at the risk of argument, I believe it is important to understand how the whole system works. Although technically some of them could have been spawned off into separate questions, each on their own only paints a part of the picture. ATC works because of a harmony of all parts, and dealing with each on it's own would be a mistake IMHO. The question might be a bit broad though.

The answer to your question heavily depends on jurisdiction which you don't specify. I will answer for Europe-Greece where I have some knowledge. The procedures might differ between the ANSPs and are subject to change.

how can the controller know that there is not another aircraft approaching out of scope range that is on a collision course with the aircraft leaving or approaching or traversing the boundary of his scope range?

There are several factors affecting that and I would say it's part of the job:
Training and personel
In Greece I know that controllers are specifically requested to setup their CWP in such a way that they can see at least 10 nautical miles from the border of the controlled area and definitely they should see the whole sector at all times. Also if some area is quite busy they have a secondary radar screen (imagine it like a PIP) that can focus in that area. That way they can have a good look of crowded areas without losing the full picture.
Also there is not one controller per sector, there are two. The RO (radar operator) and the planner. It's the planner's job (among others) to coordinate with the neighboring sectors for the trajectory of all incoming flights, and if there will be significant deviations they will notify RO.
Actual handover procedure
When a flight approaches the boundary (geographical or vertical both can happen and are valid) the RO initiates in their CWP the handout sequence. At the same time they switch the plane to the next sector's frequency. The other controller is not supposed to assume control of the flight until the plane calls them (yes there can be errors in frequency switching, that's why planes have the standby frequency on the comms panel). When the plane calls the next sector, the controller assumes control, finishes the handout sequence and the plane is officially theirs and doesn't belong to the previous controller anymore.
If the next controller doesn't accept the handout, the flight returns back to the previous sector controller. The details of that process changed after Helios 552 accident happened;(1) that's why I've said that the procedures might change at the ANSP's discretion.
There are exceptions and nothing is carved in stone:
A flight might have requests that the current controller cannot grant safely: Altitude, higher or lower. Direct to some point outside of the sector. Speed change like for example 250 knots speed restriction waiver for approach sectors. Then the controller currently controlling the flight might handout the flight earlier to the next sector with or without coordination with the next controller depending on the situation.
FIR Design
Also note that the FIR design (sectors, airways and points) is not done randomly but in such manner that there are no conflict points on the boundary of a sector but closer to it's core. So that the surprises on sector seams are minimized. See the appendix for a detailed example.
Finally, for sectors where the handover of climbing or descending flights is routine (TMAs for example), there are predefined altitudes for handover. For example a flight should be at FL210 when crossing the sector boundary. Again, nothing is carved in stone and there might be small deviations. If there are big deviations, the sectors coordinate as I've mentioned before.
Coordination between FIRs
All the above happen between control sectors in the same FIR. When handing over control to other FIRs that is a whole other story. Flights are coordinated via a communications channel, either manually (via telephone) or automatically (via protocols like OLDI). The boundary sector controller of the next FIR expects the flight on a specific point at a specific time. If the flight doesn't show up they start looking for it... They call at the expected frequency, they call at the emergency, they call the previous FIR (and not necessarily with that order).

how each centre knows who has control over the aircraft and if situations could occur where nobody is...?

There is no such thing as nobody is in control when we talk about en-route ATC. The flight is in the control of the sector (and FIR consequently) that "contains" the flight in the 3D space. The fact that you "see" the flight doesn't mean that you control it. It means that you know its presence which is a good thing.

I have to assume there is more than one human at busier control centers all working together. How is that managed? Who controls what?

Please see above the comment about RO and planner. There are also other very good answers on that specific question like this one where  you can see somewhere in the end, a

Typical sector radar team

consisting of two people, and from what I see, the left one is the RO equivalent and the right one is the planner equivalent.
Appendix I: Sector design importance explained
Here is an example from Milos sector (aka AC5) of Greece. To declutter the map, I've hidden the coastline, and displayed only the aerodromes. The sector is the black area and the rest of the FIR is in gray. Note that this is not the case in reality, I've just changed the color setup to highlight the area of interest.

To get a better idea of the area, here is what is displayed. Milos island is on the center.
Without getting into the details of the sector as this will be off topic, you can see that the conflict point I was talking about is where the red arrow is. That is MIL VOR-DME located in Milos island. There you have 10 airways(2) converging, being "fed" by Athens airport (LGAV) in the North and Heraklion airport (LGIR) in the South (green arrows). As I've mentioned, the conflict point is almost on the sector's center. It's right in the controller's eyes, away of the "ambiguity" of the sector border.
One might argue that there are 2 more points where airways converge, one in the North (KEA VOR-DME, name not shown) and one Northwest (DDM VOR-DME , name not shown) that are very close to the next sector border. Though this is true, the points are not as big conflict points as MIL VOR-DME because

KEA and DDM are major navaids for Athens TMA and it's expected to have that many airways converging towards them and
most of the flights that will cross these points over 250 (Athens TMA vertical limit) will usually be en-route, ergo no unexpected changes in heading and altitude

Also notice that Athens TMA (light coral line) overlaps will AC5. That means southbound departures from LGAV will be handed over to AC5 when they are way in the sector, away from the boundary.

Notes
(1) Many people ask how the Helios 552 accident can be related to the process. It's not related directly. Before Helios accident, the process was as follows: Propose the aircraft to next sector. Next sector accepts the proposal. Previous sector sees that and switches the frequency. That was reversed: the receiving sector is not accepting the handover unless the aircraft calls first. That way it's easier (and faster) to spot flights that for any reason did not call. As you can see, it's not directly related, but it was a change to keep the procedure on the safe side.
(2) For the record these are A10, A14, B26, B34, J56, R32, L617, M601, N134, P32
Acronyms
ANSP Air Navigation Services Provider
RO Radar Operator
CWP Controller Working Position
OLDI On-Line Data Interchange
TMA Terminal Maneuvering Area

Thanks for taking the time to write such a comprehensive answer and the link, that fully explains all the parts I was asking about which paints a full picture which was why I kept all the questions in one. :) Just to be clear with one niggly point, re: the FIR design, does that mean normally aircraft are not handed off while in a turn or climbing/descending through  another airway.

Thanks again.. I will accept this answer tomorrow if nobody comes up with a more complete one... which I very much doubt :)

@Trevor no rush :) happy to help.

Can you explain how the Helios 552 crash played into procedure changes? Seems to me that there isn't much ATC can do if the pilots aren't actually flying the plane.

@FreeMan it's not obvious at first but it's related to ATC (when pilots don't talk to you). But since this is about an accident, let me ask some people what can be disclosed or not and I'll come back. I prefer to remove the reference to the accident, than elaborating something that I shouldn't...

@SteliosAdamantidis does the Helios 552 reference still valid here?

@vasin1987 added a footnote. Hope it helps. Let me know if something can be explained better or is not clear.

@FreeMan even with almost a year delay, I've updated the answer. I hope it covers you.

Downvoter cares to explain?

I was a controller in the U.S. and think this is a good, fundamental question about ATC that is common around the world in the airspace between airports. The concept is one radar controller (and often an assistant) are made responsible for everything within a vertical and lateral boundary (a "sector" they are assigned to) that is drawn on everybody's adjacent radar scopes too. If you see an aircraft target, which also shows its altitude, you will know which sector "controls" that aircraft and can call them on the interphone if it is headed toward your own sector and is in conflict with one of your own. You know it's headed toward your sector because the other controller will "initiate a handoff" which makes it pop up on your radar screen with a blinking "handoff" indication. At that point you can look up its route of flight, current altitude and assigned altitude and determine if it conflicts with any of your aircraft for example headed in the opposite direction. That happens sometimes, and in that case you call the sector that is handing-off, and tell them to change the route or altitude assignment so it no longer conflicts with your own aircraft. They do that, and only then do you accept the handoff. In that way, every aircraft in your sector or headed toward your sector is kept separated from all the others. We call this "positive separation."

When did you retire? ATC systems worked like this 10-15 years ago, with a „blinking handoff indication“. Modern systems work with OLDI/AFTN lines and automated ABI/ACT Exchange.

@pcfreak, the system I work with today (STARS, the FAA's terminal radar display system) does "blink" the data tag of an aircraft being handed off to you.

@randomhead Oof and this still works with the modern traffic volumes? How many aircraft will you work per hour? 70? 75?

@pcfreak I'm at a very very slow facility, the most I've worked in an hour is perhaps 15-20 aircraft and that's being generous. But even at very high volume I doubt the handoff acceptance process (hitting HO, ENTER on the keyboard or clicking on the flashing target) is the bottleneck. How does the system you describe work? Is identification transferred between controllers automatically? How does the receiving controller disallow entry into their airspace?

@randomhead This is in fact really slow  We receive the flightplans for every flight planned for our centre from Eurocontrol in Brussels. They collect and distribute flightplan data. When the aircraft departs the Tower Controller will put the FPL to live by selecting „Takeoff“ in his system. An automated message is being send to the departure sector, which will correlate the track and a data label. From now on all the sectors will send automated ACT messages via OLDI lines to announce via which COP and route, at which level and with wich squawk an aircraft entering the next sector.

@randomhead If the MSG is replied to by the receiving system within 2 secs with a LAM (acknowledgment MSG) the flight is coordinated. Up to 5 mins flying time to the COP we can send (or receive) automated REV messages (revisions) changing the level. On our screen ACFT will correlate once the ACT is received and turn from a white label (unconcerned flight) to a blue label (planned flight) once flying time to your sector is <20min. You then start planning this flight into your traffic flow. If you need ACFT on a different RTE, HDG, LVL or can’t accept at all you advise upstream sector via phone

@pcfreak that sounds broadly similar to our system; the radar system will track an aircraft along its flight and will automatically initiate a handoff to the next facility when necessary. One can see the tag coming if the scope is zoomed out enough. Once the handoff is initiated the tag blinks and the controller clicks on it to indicate acceptance (approval to enter airspace). I don't know the technical details of OLDI lines and such, but unless there is an issue (aircraft is far off from planned route, etc) the handoff doesn't need to be manually initiated by the transferring controller.

@randomhead For me it does not sound familiar at all, because we don’t have what you call „handoff process“. Whenever one facility has received the flight details it accepts the flight. It all happens 100% automatic - no acceptance required. Nothing will blink, nothing has to be confirmed - also if aircraft are far off route. We can even send automated ACT messages to completely new facilities which were never on the planned route in case of long shortcuts (600nm shortcuts and more are really the standard for us; I don’t know how you handle this in the USA)

@pcf I'm still confused as to how you would deny entry into your sector if you were task- (or airspace-) saturated? Would you have to notice the inbound/planned track and preemptively call to ask that they be turned away?


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In what situations can LNAV/VNAV minima be higher than LNAV minima, such as RNP Approach to Runway 16 in Corfu?
I recently flew the RNP approach for runway 16 into Corfu. While reviewing the approach charts, I noticed something unusual. The LNAV/VNAV minima is set higher than the LNAV minima for this particular RNP approach. Traditionally, I've seen LNAV/VNAV minima being lower due to the added vertical guidance, compared to LNAV which only provides lateral guidance.
I'm curious to know the rationale behind this. Are there specific local terrain or procedural factors at Corfu airport that might explain this anomaly? Or is there a technical explanation related to the performance requirements or equipment capabilities for LNAV/VNAV versus LNAV approaches?
Furthermore, are there other airports or scenarios where the LNAV/VNAV minima are set higher than LNAV minima? What are the general circumstances under which this might occur?

RNP 16 Chart - Greece AIP

Related: Why are some LNAV/VNAV mins lower than the LPV mins for the same approach?

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Why did autopilot switch to CWS P on a LNAV/VNAV approach, and why didn't it reduce descent rate to comply with CDU alts when VNAV was re-engaged?
We were performing an NDB approach the other day due to the ILS being unserviceable.
We are flying a 737-800, FMC Update 14.0 (“common VNAV”)
We were using LNAV and VNAV as our roll and pitch modes throughout the approach. We loaded the published ILS into the FMC to be used as an overlay to the raw data. (This can be done as this approach had the identical plan view to the ILS approach. Waypoint altitudes were checked. cf. 737 FCTM)

When cleared on a heading for the approach, the PF selected the intercept heading, and the PM selected the FAF in the LEGS page with an intercept course. At this moment, the pitch mode dropped, and FMAs stated CWS P. To react to this initially, the PF selected V/S as a pitch mode (VNAV was also pressed but it wouldn’t re-engage). At 2 nm to the FAF, the PF selected the MDA in the altitude window, LNAV (wings were level), and VNAV. This selection of VNAV occurred at 2,300 ft, platform altitude 2,000 ft, 2000A selected at the FAF in the FMC CDU. The FMAs indicated that LNAV and VNAV PTH were engaged. Crossing 2,100 ft and around 0.5 to 1 nm to the FAF, the IVSI indicated -650 fpm. The PF engaged ALT HOLD to prevent what looked like a level bust, as the plane looked like it was going to continue descending below 2,000 ft.

What caused the autopilot to disengage from VNAV PTH to CWS P in the first place?
When VNAV PTH was re-engaged, why didn't it reduce the descent rate to comply with CDU altitude restrictions?

Did someone accidentally bump into one of the control columns?

I’m fairly confident that this didn’t happen. QAR data doesn’t seem to suggest that this happened either

That behavior, VNAV switching off and going into ALT HOLD or even CWS PITCH, can happen when the VNAV "gets lost" and no longer can draw a vertical path from where it is to its End-of-Descent point.
The ways that can happen are various; a wise old instructor said that in these situations, "CRZ ALT is the root of all evil" in that the FMC often is working from a cruise altitude entry that no longer matches what the pilots are intending.  And, very often I've found, the solution is to enter the current altitude (or the next level-off altitude if you're already in a descent) as the cruise altitude in the CRZ page, and then things are back to normal.  That opportunity to re-cruise the box is also a good time to specify a cruise speed like 200 or 210 knots (something above the min clean "UP" speed bug on the airspeed display); that way, you don't have the automation wanted to speed up to 240 knots (the default cruise speed below 10,000') immediately followed by a slow-down to the UP speed as you get close to the start of the approach procedure.
When the aircraft does this shift into CWS Pitch, the ideal solution is to hit ALT HOLD, fix the CRZ page, and then reengage VNAV. This sequence avoids the risk that the aircraft may descend in LVL CHANGE or Vertical Speed modes down to an altitude you don't yet want (i.e. if the set altitude is below a step-down fix that's still in front of you).
Alternatively, if you're already in a descent when the VNAV disengages, immediately spin the altitude selector to whatever altitude you can descend to now (often, whatever's associated with the first fix on the approach procedure), and descend in Level Change or Vertical Speed while you fix the FMC.  Then, once you're back in VNAV, be sure to select the lower altitude so that VNAV can descend once you've crossed that waypoint & its altitude is no longer your restriction.  (If you forget to do this, you won't get CWS Pitch, but you will go into ALT HOLD and now you're high on the descent path... ask me how I know about that scenario!)
Without having watched everything that your FMC was doing in the moments leading up to the event you described, it's hard to say exactly how the FMC got lost when you executed the new route, but virtually always, that is the cause of the behavior you observed.
EDIT, added: One other note: I've found that when one is approaching an altitude constraint (like the 2,000' in the described scenario), switching into VNAV often doesn't produce the expected altitude capture there (based on an altitude constraint in the LEGS page) the way that pilots think it will.  We expect the autopilot to capture the altitude in VNAV (with the LEGS page constraint) the same as it would in Level Change (with the altitude in the selector), but if you recently - in the last several seconds - just selected VNAV, it often doesn't.  I don't know if the VNAV logic is less aggressive in that regard, and I don't believe that this is documented anywhere, but I've seen it enough times that the description in the OP of having to hit ALT HOLD to prevent busting the 2,000' restriction doesn't surprise me.
For those following along at home,

VNAV = "Vertical Navigation" where the Flight Management Computer (FMC) will determine and guide the aircraft on a vertical path from takeoff up to cruise altitude and thence through the vertical requirements of the arrival and approach.

VNAV PTH = "VNAV Path", the usual VNAV mode (at least during descents) where the computer is working to maintain an exact vertical path.  This requires that the computer is able to compute such a path.  The alternative to this (not mentioned in the question, but for the sake of understanding) is:

VNAV SPD = "VNAV Speed", the other VNAV mode, in which the computer isn't trying to follow a path but simply to hold a given speed.  This is common in climb (get up to cruise altitude as quickly as possible), and can occur in descent too (though that's way, way beyond the scope of this answer).

CWS = Control Wheel Steering, the most basic autopilot mode, in which the pilot can make inputs via the control column, and the autopilot will then hold the attitude that has been set.  The pitch and roll modes are separate, so you can be in CWS Pitch (you're controlling the pitch via control column inputs while the autopilot maintains lateral course) or CWS Roll (you control the roll and thus the left/right path, while the autopilot holds altitude or a constant climb/descent), or both (you're almost hand-flying the airplane, except that the autopilot holds the attitude you last set). These are "dumb" but stable modes, and the last reversion before the autopilot disengages completely.

CRZ ALT = the "Cruise Altitude" entry for the FMC.  You've told the computer what altitude you'll cruise at.  Often, this won't need to be reset from the 35,000' or whatever you flew enroute, but sometimes -- especially if the programmed approach is changed fairly late in the arrival -- resetting it can be necessary so the computer can recombobulate itself.

CRZ Page = a "page" of the FMC display where information about the cruise phase of flight is displayed, and where certain entries similarly related can be made.

LVL CHANGE = the "Level Change" autopilot mode, which directs the autopilot to hold the given speed, with the power at either full climb power (if climbing) or idle (if descending).  Basically commands a constant airspeed climb or descent, getting to the set altitude as quickly as possible, with pitch controlling airspeed. The non-VNAV equivalent of VNAV Speed.

V/S = "Vertical Speed" autopilot mode, which sets a given rate of climb/descent (often, 1,000 feet per minute).  This gives a more gradual change in altitude than Level Change, with a more shallow deck angle (which flight attendants pushing carts up & down the aisle appreciate).

ALT HOLD = "Altitude Hold", the autopilot mode in which the autopilot holds an altitude, either the altitude the aircraft was at when the ALT HOLD button was pressed, or what was set in the altitude selector if you reached it in LVL CHANGE or V/S.  Operating in VNAV, you don't normally see this, as VNAV Patch includes level segments (i.e. the defined path includes an hour at 35,000' before starting the descent).

PF = “Pilot Flying.” Captains and First Officers will assume the role of flying or monitoring that sector.

PM = “Pilot Monitoring” - also previously referred to as “Pilot Not Flying.” “Monitoring” is a better word from a CRM sense as “not flying” gives the impression that this pilot is passive, whereas they are still a very active and important in the multi pilot operation.

Thanks. Do you think VNAV “getting lost” might have been associated with the PM doing an update to the CDU with an intercept course to the FAF?

Just doing an intercept to a course isn't enough by itself to cause this, but my thought would be that something else that changed when executing that update likely could have been.  For instance, if there was a fix with an at/above altitude on the final ahed of you, but the aircraft was already below that altitude, that's a "VNAV gets lost" case, even if you delete that altitude subsequently. (Not suggesting that's what happened in your case; that's just an example of things that can cause it which happen at the same time as EXECuting the intercept.)

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What is the meaning and origin of the phrase “dead band” in relation to flight controls?
A quote from the Boeing 737 NG FCTM:

With both hydraulic systems A and B inoperative, the ailerons and elevator are
controlled manually. A noticeable dead band will be observed in both of these
controls. High control forces are required for turns and the control wheel must be
forcibly returned to the aileron neutral position.
737 NG FCTM (Boeing) - 8.21 Manual Reversion

I have the 737 systems knowledge and concept of high control forces if hydraulic systems A and B were to become inop. What I do not understand is the meaning of the second sentence above - “a noticeable dead band”
What is the origin and full meaning of this phrase, “…dead band will be observed…?”
This phrase is also used in relation to other aircraft, for example F16’s as seen in this answer

Deadband

The dead-band in a flight control is a region of travel where stick movement does not result in control surface movement: a zone where stick input is dead.
With hydraulic power ON, moving the stick opens a servo valve, upon which hydraulic fluid starts to flow from the actuator, which moves the elevator. There is a follow-up mechanism in the mechanical linkage that closes the servo valve again when the corresponding elevator position is reached.
With all hydraulic power OFF, the elevator needs to be moved by human push/pull power. But when moving the stick, it travels within the actuator servo valve band first. Only with the servo valve running into its end stop is there a direct mechanical connection between stick and elevator - but only in one direction.
So from neutral:

Start pulling, nothing happens with the elevator (a dead-band).
The servo valve hits the end stop, and now the pilot may feel the aerodynamic forces on the elevator, which they pull against further to create a nose-down input.
The pilot then reverses direction and pushes the column, which moves the servo valve out of its pull direction end stop.
Nothing happens until the servo valve hits the push direction end stop (another dead-band).
And now the applied push force results in elevator movement in the nose-up direction.

There are more effects at work, like the airspeed, the speed with which the stick is moved, internal friction in the control loop etc.
The friction forces in the cable loop are considerable, the aerodynamic hinge moments are fed back to the flight control, and there is this dead-band - all making manual reversion quite an experience.

 Technically, the pilot feels the aerodynamic forces on the elevator (and/or aileron) control tabs, not on the elevators (and/or ailerons) themselves; the elevators and ailerons are controlled aerodynamically in manual-reversion flight by deflecting their respective control tabs.

@Vikki Yes indeed.

Unfortunately I am not able to write a comment and I am not sure if this answers your question.
There is a Wikipedia article about this.
There is a range of inputs via the stick/yoke (making very small adjustments), which won't change the ailerons or elevators deflections. This is a problem of the FBW system compared to reversible Control Systems, because there is no "mechanical" coupling between them.

RE "This is a problem of the FBW system"-- I clearly remember some recent ASE answer that noted that a "dead band" was intentionally designed into the F-16 sidestick (or was it perhaps the F-18 Hornet?}

Ouh, I havn't read that answer yet. AFIK some filters are added also on the control system so you can delete not wanted frequencies e.g. Notchfilters on structural frequencies, Commando Filters for PIO Problems (overshooting), Washoutfilters.
But there is so much more to study, since I am not at all an expert in this field. ^^ Some Sources: https://en.wikipedia.org/wiki/Washout_filter
https://www.mathworks.com/help/control/ug/yaw-damper-design-for-a-747-jet-aircraft.html
https://www.researchgate.net/publication/238690397_FILTERING_STRUCTURAL_MODES_IN_AIRCRAFT_NOTCH_FILTERS_VS_KALMAN_FILTERS

@quietflyer The F16 side stick had some spring loaded deflection designed into it to indicate the end of useful control travel. Usually a deadband refers to a control travel region without any spring loading, only some friction, in which the control deflection does not result in surface movement.

It's that empty region where you can "wiggle" the stick and not actually push it.
Germans call it "Luftigkeit", and english translation would be "airiness".
It's not a thing in aeronautics only. You may observe that in other things, like (a bit older) gaming controllers, car gear lever, common faucets, ...


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What is the optimum speed for takeoff flaps?
I took a 737 rating written test yesterday and one of the questions was:
What's the optimum speed for takeoff flaps?

V2
V2 + 10
V2 + 15
V2 + 20

Anybody knows the answer? I did some research and couldn't find it.

Optimum for what? Climb gradient, rate of climb, engine-out climb, schedule?

@Sami I have no idea. This was the exact wording of the question as far as I remember.

FWIW, the webpage at http://www.flaps2approach.com/journal/2014/8/4/boeing-737-800-takeoff-procedure-simplified.html has the statement, "V2+15/20 is the optimum climb speed with takeoff flaps.  It results in maximum altitude gain in the shortest distance from takeoff."

I assume the question means optimum climb speed.
From the Boeing 737 NG FCTM (3.30 Takeoff and Initial Climb):

V2 + 20 is the optimum climb speed with takeoff flaps. It results in the maximum
  altitude gain in the shortest distance from takeoff. Acceleration to higher speeds
  reduces the altitude gain. If airspeed exceeds V2 + 20 during the initial climb, stop
  the acceleration but do not attempt to reduce airspeed to V2 + 20. Any speed
  between V2 + 15 and V2 + 25 knots results in approximately the same takeoff
  profile. Crosscheck indicated airspeed for proper initial climb speed.

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text:
Is it a common airline practice to base T/O speeds on the actual T/O weight when an assumed temp thrust is used?
Let's say the current outside air temp is 15 C and you have decided to use 50 C as the today's assumed temperature for your takeoff. In this case, use of the T/O weight the assumed temp thrust supports gives you the balanced V1.
But our company rules are to use the T/O speeds of the "acutual" T/O weight instead of those that the T/O weight the assumed temp thrust applied provides. I assume this rule has been made to give a greater safety margin for a runway overrun in the event of a possible rejected takeoff at the expense of decreased obstacle clearance, since use of the actual takeoff weight invariably brings lower V1, Vr, and V2 speed than when the T/O weight of the assumed temp thrust is used. My question is: is it a common practice among commericial airlines to use the actual T/O weight instead of the assumed temp T/O weight?

Assumed temperature is simply a way to reduce your thrust to some predictable amount that you can still find in the charts. I've never heard of using an assumed weight for 737 performance. Fictitiously adding weight reduces assumed climb performance, which serves no good purpose. Can you give an example of how much you see "assumed weight" differ from actual weight?

Finding the weight (at whatever thrust setting you're using) that produces a balanced field isn't about "assuming" the airplane weighs that much, it's simply determining how heavy you could be to still meet all performance requirements. Base your takeoff & climb speeds on what you DO weigh + whatever thrust you ARE using (even if that thrust setting is being reduced based on an assumed temperature). No good comes from using a low V1 and high VR with a light jet & long runway just because that's the V1 & VR that you'd have with 40,000# more weight!

In my understanding the idea of the assumed temperature method is to calculate the whole takeoff as if it was as hot as you‘re assuming. That gives some margin on the day due to the true airspeed (and thus distance covered in a given time) being a bit lower than assumed. Mixing normal temperature speeds into it, especially V1, might not be conservative (I‘d have to think about it a bit more!). The only exception are VMCG and VMCA which have to be calculated at actual temperature, obviously. By the way, whether it’s a common practice or not won’t be easy to answer - only whether it’s safe.

@Cpt Reynolds "Mixing normal temperature speeds into it, especially V1, might not be conservative." At the balanced V1, the accelerate-stop distance and accelerate-go distance equal to each other. As the V1 decreases from the balanced V1, you need a less accelerate-stop distance, while you need a greater accelerate-go distance. Granted that's the case, doesn't a lower V1 always give a greater safety margin at least in terms of an overrun in the event of a reject takeoff?

@lemonincider Yes indeed. I would in that case be concerned about the accelerate-go case, where the aircraft has to complete the engine-out takeoff from lower speed than the balanced full-thrust V1, but only using reduced thrust. As I said, it’s entirely possible that’s OK, but it doesn’t feel right to me. I would have to think about it some more before being certain.

@Cpt Reynolds Thanks for your input. My concern is that it might give a greater safety margin for an overrun, but as you have pointed out, it puts the aircraft at a speed lower than V2 when it leaves the end of the runway and hence potentially a less obstacle clearance. This way of calculating V speeds is applied regardless of the airport environment in our company, and I'm worried it undermines safety in some airports surrounded by high obstacles.

@lemonincider Yes, I share your concern. Boeing‘s recommendation when I attended the performance engineering class some years ago was indeed to unbalance V1 if allowable in order to increase margin on rejected takeoff (as flying is the less risky manoeuvre than aborting - after all, it is practiced much more often). However, I don’t believe the technique described by you is what they meant!

Actually - can you clarify a few points in your question, please - are you using the takeoff speeds for the actual temperature and a higher weight, or those for the assumed temperature and actual weight? Are you getting the speeds from a runway weight chart or from a software tool in the widest sense - i.e. through EFB, ACARS etc? Working on a response, but trying to get it right...

@Cpt Reynolds We get the assumed temp to use on each flight from our airport analysis charts and use the takeoff speeds which correspond to the actual weight rather than those the weight the assumed temp supports gives. The weight the assumed temp supports is invariably higher than the actual weight because it factors into all the disadvantageous conditions like tail winds, QNH lower than standard, and slippery runway conditions.

@lemonincider The runway analyses I know always show each runway on a page, rows for temperatures and possibly columns for conditions or wind. Are yours different?

You determine the t/o thrust as a function of t/o weight and runway length
Once the t/o thrust is determined you can select the assumed temperature on the thrust limit page on the CDU.
V1 is not the target primary parameter, it is a consequence of the calculation, on modern FMS your calculated value is cross checked with a range calculated by the FMS, that is your calculation could be rejected by the installed FMS unless you may force your value on some models.
A minimum rate of climb is necessary with a speed of V2+10, and at worst V2 with engine failure.
Backward of this Vr is computed.

I don’t think that is an answer to the question...?

@Cpt Reynolds, As far as I know no pilot will decide to use the assumed temperature ahead of every thing. This is a decision that is taken once you have already calculated the required thrust. On the other hand V1 is a consequence of V2 which itself is a consequence of the weight. So after calculating the required minimum thrust, then you may decide to use an assumed temperature if possible. So I am answering to the question, otherwise why not?

Well, the decision to use assumed temperature or not could influence the value of V1, maybe even V2 in some cases. The question was whether it is common practice to use non-assumed-temperature speeds when flying an assumed temperature takeoff (this question only makes sense for cases where the speeds are different between both options). So I don’t think explaining the calculation process answers the question about how commonly a different „mixed“ process is used...

Of course you have to understand the calculation process otherwise you will not understand why high assumed temperature will be rejected as not producing a compatible V1

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
How do pilots maintain level flight after launching missile?
I saw, on National Geographic, two well built navy guys lifting a comparatively small missile to be attached on wings of an F-18 Super Hornet.
So when one missile on left wing is launched doesn't it drastically shift CoG of jet? Who copes with this shift

Computer & other stuff internally adjusts the zero position of flight controls to attain level flight. In this case what is the basis of detecting shift in flight control made by pilot - the old zero or the new zero?
The pilot by shifting position of flight controls, using hands & feet, in non-zeroish positions to maintain level flight despite changed CoG. If yes, isn't it detrimental to pilot's performance in a dog fight?

One would also need to consider the change in lift when the departing missile effectively changes the shape of the jet's wing.

It's called roll damping and inherent stability. Yes, the cg shifts, but the aircraft will not spin out of control, but will make tiny attitude adjustments and fly on much as before.

Some stores on aircraft actually have substantial G-limits on them, especially when asymmetrically loaded.  In this case, those stores would be jettisoned prior to engaging another aircraft in a dogfight.

It's kind of a mix of the two. Flight controls on aircraft have what's known as trim. All (or nearly all) airplanes have elevator trim; many also have rudder trim and aileron trim. The trimmer for each control is used to balance constant forces needed on that control.
To take an example that's more widely applicable than launching missiles: when you increase power (to climb or to reach a faster airspeed), the airplane will have a tendency to pitch up, so you might find you need to push forward on the stick to maintain the right attitude. By moving the elevator trim forward, you eliminate the needed force, effectively changing the neutral position of the stick.
On early aircraft, the trim often worked by having springs connecting the control wires to a large lever. Working the lever pulls the spring in that direction, applying a force to the controls. On modern light aircraft, there is a trim tab on each control surface. The trim tab is like a tiny control surface on the control surface. Moving the trim tab to one side or the other provides a force on it, replacing the force the pilot would provide through the controls.
Fly-by-wire aircraft, such as military jets and large passenger airplanes, have electronic trim. Since the pilot doesn't have to put much force on the controls to work them anyway, trimming just resets the neutral position of the stick as you describe. Because it's electronic, there can be different ways to control it. Some aircraft still have small levers to set the trim; some have up/down buttons in reach of the stick (such as the Su-27); and yet others simply have a single button that trims to the current position of the controls (the A-10). As Mr Çetin points out, some very modern military jets take advantage of the possibility of computer control: the aircraft is aerodynamically unstable, but a flight control system manages keeping stable flight.
Returning to the particular case of the F-18, it doesn't re-trim itself. When heavy ordnance is launched, the aircraft will roll to one side as you suspect, and the pilot has to compensate with the stick and pedals. Once he has stablised the aircraft at the desired attitude and airspeed, he can adjust the trim using a hat switch on the stick.

Regarding the F18, you might be surprised to know ordinance doesn't affect the aircraft much at all--other than making it a slow G-limited pig.  I've never retrimmed the jet after dropping.  It's a pretty incredible aircraft, the computers are magical.

@RhinoDriver that's cool man, I wish I could get some experience like you :)

The F-16 Fly-By-Wire (and therefore most likely also the F-18) does actually not automatically correct for left/right CG shift due to stores load. The pilot manually has to adjust the electronic trim control (which Dan Hulme already described) to account for it. However the CG shift from releasing of one missile is relatively minimal, and would require only a tiny trim adjustment. Bombs or larger air to ground missiles is a whole different story.

Can you state your source please? Or are you an (ex) fighter pilot?

BMS 4.32 Dash 1 - F-16 manual for the F-16 Simulator Falcon 4.0
While not a real life manual, vast majority of systems are accurately modelled to how it works in real life.
see section 1.12.7
http://www.candyparty.com/ST/Download/Checklists/BMS/Document/BMS432_dash1.pdf

The Shrike (AGM-45)
Was on a training exercise where I got to launch a Shrike at a ship based radar target. It was a big missile and a lot of fun launching.

Weight:  390 pounds
Length: 10 feet
Diameter: 8 inches
Speed: Mach 1.5

I felt it come off the aircraft and made only very minor adjustments to the flight controls. I remember there being a bit of yaw, and not so much roll. I was mesmerized by its departure. It got kicked off the pylon and dropped slowly away from the wing keeping pace with me, before the rocket ignited leaving a long trail of smoke and disappeared.
The controller of the boat told me when the radar came up, and I saw the Shrike lock on. With a positive acquisition, and clearance to fire, I made a call that the missile was armed and inbound. They had an idea when it would arrive, although they were not tracking it. They had a calculated flight time and shut down the radar before impact. The missile went ballistic and missed the target.
Some pilots would fire first and then wait a few seconds before calling armed and inbound. In this way the controllers would misjudge the flight time allowing the missile to destroy the target. Since several flights used the target, it was somewhat customary for the last flight to make an early inbound call.
During the brief we went over the launch procedures and there was a warning that the pilot should not fly through the plume of the Shrike because of how hot the gas was. As the missile left the aircraft the plume ended up down the intake, I corrected quickly and looked in at my turbine outlet temperature (ToT). It was pegged, and my initial reaction was, "Holy $%&^" Then I settled down and realized it was a guage malfunction. Relieved I headed home and let maintenance know.
An Air Medal
I was briefing with one of the Cmdrs in the squadron and he was in his khakis with his ribbons on. I never kept track of those sorts of things, and yet was interested in a simple gold and blue ribbon in one of the rows. "Hey, Bagrat what is that one for?"
He told me that while in Vietnam he was out in front of the strike with 4 Shrikes on his wings. His job was to light up the SAM sights and engage them with his anti-radiation missiles. As he moved inland his ECM gear went off and he had a target acquisition warning followed by a visual of the SAM that was launched.
He launched the first Shrike and broke on the missile, while the radar that was tracking him shut down. When the Shrike lost the radar signal it went ballistic and missed the target. As the missile went by him he turned back towards the site and was picked up again by the acquisition radar. Another SAM was launched, and again he fired and broke to get away. The radar site shut down once more coming back up when the Shrike missed them. Finally, on the fourth and last Shrike, he got a hit on the site. He won the Air Medal for that engagement.

inspiring words, makes me wanna be a better engineer.

The f-18 is a fly-by-wire aircraft. This means its automatic flight control system takes care of stabilizing the aircraft for cg changes, or other sudden forces (turbulence, bird strike, engine loss, etc). The controller keeps the aircraft in a balanced ("trim") state and allows the pilot to maneuver the aircraft even in the presence of these sudden changes. Therefore the pilot would probably not feel the mass leaving the aircraft, and would not have to worry about which side the
Missile left (can be right or left wing).

So when one missile on left wing is launched doesn't it drastically shift CoG of jet?

Not always. Aircraft are designed so their stores are as close to the CoG as possible specifically to reduce this. And that's true for a Cessna as much as an F-15.
Putting the stores at the CoG isn't always possible; it made swing-wing designs rather complex, for instance. In other cases, practical considerations get in the way. Many 1950s interceptors had their stores in less-than-ideal locations (cf Lightning and Avro Arrow) but the relatively light weight of the weapons made this less of a concern.


text:
What is the feasibility of a Coanda/Magnus effect wing airplane?
It seems the EU granted some hundreds of thousand € to a non-engineer, to study a cargo airplane with a turning cylinder in the leading edge, to produce increased lift by the Coanda/Magnus effect also used in the Flettner rotor sails for ships. As the concept seems having been discarded because of the important gyroscope effect of the turning barrel: anybody commenting about technical reasons for this revival of a discarded concept?

The answer to this can only ever really be speculation. The researcher's hope, however, seemed to be that modern composite materials meant that the extra lift could now compensate the extra weight. The big problem other than weight (which was never solved), however, is that if the aircraft loses power it loses lift, just at the moment it needs it most.

Can you include references in your question?

An historical report about Magnus/Coanda wing airplanes exists in the German publication: 'Luftfahrt', nr 22, pag 3415-3430, Dipl. -Ing H. J. Lindstaedt (Lindstädt), 'Flugzeuge mit Walzenflügeln', Mittler & S. GmbH, Herford, 1978, ISBN 3 87547 185 7                                          Some info is in the Wikipedia article: 'Fanwing', including the reference/link to a review technical article in english (offered to be purchased)

A lot of research grants are wasted on scams or projects making exorbitant claims. See it this way: The people who judge an idea grant-worthy need to spend the money they have available somehow, and if they were clever enough to pick winners all the time, they would not work in a government bureaucracy.
On the other hand, who is to judge what idea is really good before it has been tried? You have to accept some losses if you want to move outside of safe bets - only then can new ground be broken.
NASA funded a researcher for more than three decades who was only working on joined wing projects. It's easy to see that they are a non-starter, but this guy built his career on that particular hoax.

Agencies get money, if not spend in year, amount they get next year is reduced. Also, there's a patent for a 5-Stroke, double expansion Int Comb Eng, US 2002/0050253 Schmitz. Bourgogne Uni, P Leclaire, worked on it, Otto build the same: 1879, CT company EHV build car with this type of engine, 1906 (T Suzuki), 2 Spanish patents: 0156621, 1942,  Jimeno-Cataneo; 0433850 Ubierna-Laciana 1975, on the same. Somebody applied for patent Wankel Engine Rotor, but was described 1982, D W Garside SAE paper. 'Fanwing', had EU grant: see Wikipedia: 'Fanwing': 'A review of Magnus effect in aeronautics'.

J. WOLKOVITCH.  "The joined wing - An overview", Journal of Aircraft, Vol. 23, No. 3 (1986), pp. 161-178.
https://doi.org/10.2514/3.45285 Is this? Or this one:
NASA-CR- 172529 , 19850008520 'Aerodynamic-Structural Study of Canard Wing, Dual Wing, and Conventional Wing Systems for GA Applications' BP Selberg, DL Cronin. University of Missouri, Rolla

@Urquiola: Yes, of course, Julian Wolkovitch.


text:
How do fighter pilots manage food, drink & toilet?
There doesn't seem to be any place to bring food or drink.
And what about WC?
And for single seat combat planes?

in their pants if they really have to go

Gliders pilot can drink directly in bottles or use a camelbak. They still can eat regular sandwich as they don't have any mask. They also use adult diaper to pee. Formula one's helmet is equipped to drink while piloting. Fighter pilots may use the same techniques.

Yellow ice over Russia.

Life Strapped to the Rocket
Food and Drink
Fighter pilots do not have any problem taking food and drinks on flights.  The biggest concern is to prevent foreign object damage (FOD) from items like crumbs, bottles, bags, etc.  Otherwise, there are plenty of places to carry food to eat: your helmet bag, G-Suit pockets and flight suit pockets.  I typically carry water with me in my g-suit pocket, and don't worry about food unless its going to be a long flight.  Thankfully, training missions are rarely long enough that they require food in the cockpit, and it mostly just applies to deployments.  Typical food usually includes protein bars, chocolate, cereal bars, etc.  We try to avoid small loose foods like peanuts and M&M's because they could easily spill and FOD the cockpit.
Depending on cockpit altitude, the mask can be easily removed to either eat or drink.  However, fighter cockpits are only partially pressurized, and, in the Super Hornet, there are times when cockpit altitude can be as high as 20,000ft.  Sound judgement is required before removing your mask.
Edit: I've also seen guys incorporate camelpacks into their harness/vests as well.

Restroom
Obviously life on board a fighter jet is cramped, and there isn't a lot of room to move your body, much less use the restroom.  In addition to water, on every flight I carry an item called a pittle pack.  As its been stated, its a plastic bag with powder in it that reacts to urine.  The powder and urine mixture then turns to a jelly that helps prevent spillage, and the entire bag then rolls down and seals on itself.
Pittle packs present 2 major problems (three for carrier pilots):
First: Where the hell do I put this bag of urine? There isn't a lot of storage space on fighter aircraft and nobody wants to put a bag of urine in their g-suit pocket or helmet bag.  Sometimes you can get away with placing the bags in the flight publication pockets, but you better be sure it doesn't fall out.  The last thing you want is for the bag to fall, break, and then to smear about the cockpit as you continue with your mission.
Second: How do I get my junk out of this rocket powered chastity belt? My harness is strapped tightly 8 ways to the ejection seat, which is also cinched tightly to my g-suit.  My g-suit has an opening for my crotch, but its tightly zipped into position over my flight suit.  My flight suit has a zipper, but as stated, the zipper is covered by the g-suit.  And just to add one last layer of difficultly to this impenetrable force field, I've got to dig myself out from between the folds of my boxer briefs.  Success! I've managed to free myself only to discover that the tip of my business end is only barely protruding from this labyrinth of zippers and belts (size may not matter in the bedroom, but it sure as hell matters right now).  The next question you have to ask yourself is, do I have enough time to keep digging, or do I need to attempt to arc it into the bag?  Choose wisely.
Third (The carrier pilot):  Boom, OK three-wire trap!  Ah , the Naval Aviator.  I drop bombs, piss in bags, and then return home to land on a boat.  I'm pretty much a boss... and I'm covered in piss because I didn't secure my pittle pack before trapping on the boat.  The bag, upon catching the three-wire, like a boss, rocketed across the cockpit and smashed against the bulkhead, exploding all over my legs.  Always remember to secure your pittle packs before trapping on the boat, because even if your buddies didn't see it happen, you can guarantee the ground crew will tell them all about it.
Our female counterparts are forced to wear depends, I don't envy them at all.  Brave souls.
Oh, and if its not pee, RIP.

RIP = Rest in Piss?

@MarchHo you got the first two words right... The last one isn't Piss and rhymes with Loop

So I wonder, as a male, you've never considered the adult diapers? (I hope you don't mind me asking)

@yo' haha, nope.  Just the thought of sitting in my own filth makes me squirm in my seat.  You've got to remember that the fighter crowd consists largely of prima donna's--myself included ;)

"urine jelly". Both the worst, and most hilarious thing to cross my mind all day.

I'm a former F-15 crew chief. I've recovered a plane that had a pilot 'RIP' as you put it... it is surprisingly difficult to order a replacement seat pad for an ACES-II ejection seat. Fortunately, it was BioHaz that got to do the initial cleanup, but that pilot had a new nickname among crew-chiefs after that.

@RhinoDriver This entire answer seems like it was written by the author "A Lot of Experience Concerning These Issues."

In WWII long-range propeller fighters were usually fitted with an extraction tube, basically a pipe to pee into. This typically froze up in the cold, so you'd have to be pretty desperate. This is why Chuck Yeager said it was vitally important to pee before going on a mission.
Single seat fighters these days don't have any kind of facilities for that, pilots on long-range missions carry either a bag with absorbing gel in it or a plastic container with the same material in them. The USAF's nickname for these are "piddle packs". As for eating it's generally field rations, protein bars, candy bars, anything that is compact as space is an issue.

I generally see fighter pilots in movie and TV wearing masks (I assume they're oxygen masks). Do they just have to take those off and deal with insufficient oxygen while they eat? Do they fly to lower altitudes to eat?

@raptortech97 they wear the mask but can remove it to eat or drink for a bit. It's just more convenient to keep it on as it contains the radio microphone for example (and might be somewhat fiddly to remove and put on wearing gloves).

@raptortech97 Depending on the mission they are flying, the mask isn't required for oxygen.  Fighter aircraft are also mostly pressurized (although not to the same degree as a commercial airliner).  And they can still get some oxygen if the put on positive pressure on the regulator and have the mask hanging close to their face as they eat.

Fighter pilots wear masks because the small cockpit means a decompression at altitude is much more likely (read: certain) to result in immediate loss of oxygen supply, whereas in an airliner you have a few minutes to fit a mask.

@user19555 Fighter aircraft are only partially pressurized.  Cockpit altitude can get as high as 20,000ft in the super hornet.

The U2 has a kind of toaster for heating ration packs.
Funny story told to an ex-RAF friend of mine when he was based in Cyprus:
Guy on a U2 mission over the USSR puts his lunch on and carries on with the mission. Suddenly he heard an enormous bang and his canopy was covered un red stuff.
He panics thinking he's been hit, starts looking everywhere for damage to both him and the aircraft (one would presume he put the lack of pain down to adrenaline).
After a while he realises there is no damage and he is not hurt. Turns out he had forgotten about the tomato-based thing he put in the heater and it had violently exploded.

Related to this, I think I read somewhere that SR-72 pilots would just put their ration pack against the cockpit window, which was so hot at Mach 3.whatever that it would heat up the food quite nicely, thank you very much.

Yeah, the U2 was strictly subsonic in addition to high altitude, if you tried the same trick you'd likely freeze your food, not cook it. I'm guessing the cooking apparatus was a hack based on the cabin heater, which is necessary at the U2's service altitude even with pressure suits and a pressurized cockpit.

FWIW, it is not just fighter pilots that have this issue.  Many small private planes have facilitates to relieve one self.
My Cessna 340 had a relief tube with consisted of a narrow funnel with a trigger valve.  You put the liquid (I will leave it to your imagination how you got it there) into the funnel and pulled the trigger.  This opened the valve connected to a plastic tube that exited the aircraft under the tail.  Since the cabin was pressurized there was a pretty descent pressure differential that resulted in a quick evacuation of the funnel.
For aircraft without such systems there are wee-packs that a pilot can buy.  These contain a funnel area (they have different shapes and sizes for men and women) attached to a bag.  The bag contains a powder that turns into a jelly trapping the liquid.  When the flight is complete you dispose of the pack. See this product for an example.

"exited the aircraft under the tail" - how appropriate.

what if you pull the trigger with your business end still inside the funnel?

SR71 crew would heat their meals by pressing them against the windows, as they were hot enough to burn fingers if the glass was touched. The crew would then eat with the helmet open. The SR71 was pressurized not for crew comfort, but rather to cool the electronics!
Fighter pilots, like the Mercury and Gemini missions, wear adult diapers in flight. As the joke goes:

What does the inside of an EVA suit smell like?

"Depends."

I believe that it was Alan Shepard who famously ruined some on-board electronics when his pee shorted them out.

Alan Shepard was grounded for several years in the US space program due to Ménière's disease. (Also here.) While it is linked to excess of fluids in the inner ear, I don't believe that's what you are referring too.

The Shepard story sounds like an urban legend. The urine of a healthy person is more or less sterile so getting pee in your ears shouldn't cause an infection unless you already have a UTI.

I did mention the pee story as "rumor". In fact, I cannot find a mention of it online. I'll remove that bit.


text:
How much time does a landing/take-off add to an otherwise direct flight?
I'm interested to know how much time a descent and ascent to cruise altitude takes as part of a longer journey.
A standard jet-aircraft (for example a A340 or 777) flies for eight hours from City A to City C. While doing so it flies over City B.
Now the same jet flies from City A to City C but as it approaches City B it descends and lands at B. The plane taxis to the gate. As soon as it's there it pushes back, taxis, takes off and returns to cruise flying to City C.
Approximately how much time is added to the journey by virtue of having descended, landed, taken-off and climbed back to cruise? Assume no ATC delays etc.

Let's take the best case scenario to start with, and assume that the cruise ground speed of the airliner is around 400kts.
For our best case, we also assume that the runway is lined up with the flight path and that the airspace is quiet so the plane is cleared "straight in" with no vectoring for separation or holding patterns.

Descent:

A typical descent profile would start 100nm out, during which the plane would slow pretty uniformly from around 400kts to around 140kt. This gives an average groundspeed of 270kt. So this 100nm is covered in around 25 minutes rather the 15 minutes at full cruise.
The descent has cost us only 10 minutes.

Taxi and turnaround:

At a smallish (and well designed) airport the rollout and taxiing to the stand may only take 5 minutes, plus another 5 to attach the air bridge/stairs and open the door. Passenger and baggage turnaround would typically take around 30 minutes, but you have specifically excluded this in your question so we can ignore it. Then getting departure clearances, startup and taxiing to the active: say another 15 minutes.
So this phase has cost more or less 25 minutes.

Take off and climb out:

Again assuming we're cleared for immediate take off, it takes around 20 minutes to climb to cruise altitude, at an average ground speed of (say) 200 knots. This means we've covered about 70 miles, which the cruising aircraft would have covered in just over 10 minutes.
So this final phase has cost us another 10 minutes.
Total for the best case scenario is 45 minutes.
Of course the best case is not that likely. If the airspace is busy, holding for another 10 minutes before final approach, and 10 minutes further wait for departure and takeoff clearances, would not be surprising. And if the active runway is in the "wrong" direction or vectoring is needed for traffic or noise reasons, that can easily add another 10 minutes or so.
So in the non-best case scenario, a total loss of 1h15 to 1h30 would not be unreasonable.

Excellent answer, thank you.

Great answer, thanks. I'm wondering if the total added time makes sense, given that many short flights take 1h10 (e.g. Zurich-Nice) and still have to traverse 400km/215nm

I've compared the scheduled flight times of URC-TSE-SVO (where the non-stop URC-SVO flight directly overflies TSE), and the extra time needed seems to be around 30 minutes. How can it be possible?

Either one or more of my estimates/assumptions was wrong, or the two flights have different flight profiles (speeds/altitudes). Eg without looking, it's possible that the direct flight was flown at a slightly slower speed to save on fuel.

I was curious if I could find other sets of cities exhibiting this behavior. SFO-DEN-PIT offers an example. Quoted times vary slightly across airlines: SFO-DEN (2hr 30 min - 2hr 40 min); DEN-PIT (2hr 50 min - 2hr 58min). Selecting UA, we have SFO-DEN at 2hr 37 min, DEN-PIT at 2hr 56 min, and SFO-PIT at 4hr 47 min, for a total loss of 46 min.

The best-case scenario is generally common, for brief, planned refueling stops.


text:
Do small business jets have HEPA filters?
Do small business jets (Phenom 300 for example) have HEPA filters for recirculated air? Or don't they recirculate air at all?

Embraer's own website confirms that their business jets can recirculate or draw fresh air, but HEPA filters don't seem to be an option until you get into the Praetor size and above -

In addition, the now standard HEPA filter for the Praetor jets can
capture 99.97% of bacteria, viruses, and fungi — further providing
fresher, cleaner air inside the cabin. So when you fly on an Embraer
business jet, you can breathe easy.

Thanks for your answer! This information on the website seems a little confusing, since it does not specify if the recirculation exist in their smaller jets or if it's only a Praetor feature. It also seems a little strange to me to not filter at all the recirculated air.

@PedroGuimarães: I would be surprised if they didn’t have SOME kind of basic filter for recirculated air. It just won’t be rated for hazardous airborne particles like HEPA filters are.

Can you add a quote from their website and link to the relevant page(s).  That would greatly improve this answer.

Since HEPA filters are common, an after market kit may be readily available.  The filter just needs to be in the cabin airflow duct, with appropriate specs for flow.


text:
Replacing or supplementing turbofan with electric fan
Could you replace 2 B747 engines with electric turbofans? Could the 2 standard turbofans produce enough power to allow electric cruise with jets used for take off?

Answer to the first question: yes you could, and the answer to the second would be theoretically yes, but it would make no sense. Here's why:
When designing aircraft, a simplified version of choosing the engines would be that the plane should be able to safely climb with half of the engines installed. So: cruising power is significantly less than T/O or climb power. Basically this imaginary hybrid 747 would be able to cruise with two engines only, be they electric or conventional.
If the question is about generating electricity with the 2 turbofans, the problem is that to provide electricity for the electric fan so that it could maintain cruise speed, the conventional engines would, of course, have to be running at rather high power setting, and therefore they themselves would provide enough thrust for cruise. Assuming (quite liberally) efficiency of 90% for both the generators and the electric motors, we would end up with a maximum efficiency of 81%. At least 19% of power would be lost along the "powertrain".
If the electricity for cruise was to come from batteries, the setup, simply put, will not work. The weight of the huge battery bank is way too heavy for economical operation.
A little more sensible setup would be one where conventional engines are assisted by electric fans or such for takeoff and climb, and the electricity would come from batteries. Here again, hauling a heavy battery set for great distances is not very efficient, even if the battery bank could be smaller in this case. in addition to this, the electric fans would cause drag during cruise if the electric propulsion system is not integrated into the conventional engine somehow.

It is better to have an electric boost for departure, with jet core optimised for high pressure ratio at high altitude.

big EMAL accelerator built into runways :-)


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Is it possible for a pressure loss in the cockpit to not extend to the cabin?
I have done research into the question of pressure differences between the cabin and cockpit and the theoretical answer I receive the most is that the pressure difference would equalize almost instantly, as cockpit doors are not capable of an airtight seal — and it makes sense, but I recently came across an incident that happened a couple years ago: Sichuan Flight 8633.
On that flight, the windshield actually exploded, and based on the passenger recordings, the cabin seemed a little messy from objects flying around, but they could still hold onto their phones and the flight attendants were able to stand up.
The only comment I could find on that matter had to do with insulation and sealing that protected the passengers from the low temperature and pressure loss. So with that information in mind, is it possible for a cockpit to experience extreme loss of pressure while the cabin suffers minor loss of pressure as on Flight 8633 (an A319)?

As far as stews standing up or passengers holding their phones, that wouldn't be effected by pressure loss, but by wind. Since the cockpit door held enough to keep the temp in the main cabin up, it was also resistant enough to wind to keep from blowing things (or people) around.

As the answers have pointed out, the premise of this question is incorrect: there was no pressure differential on flight 8633.

The internal walls in an aircraft are not designed to withstand any significant pressure difference. Since the accidents of American Airlines flight 96 and Turkish Airlines Flight 981 where explosive decompression in the cargo hold caused the passenger cabin floor to partially collapse and damage the control cables running below it, the internal walls and floors are intentionally designed so that the pressure has a way to equalize without causing damage to any of them (with enough openings or loosely fitted panels that will blow out if needed). Therefore it is not possible for pressure loss in cockpit not to extend to the cabin, or the cargo hold.
The information I found about Sichuan Flight 8633 only says the passengers were not exposed to cold, nothing about pressure. During decompression, the air rushing out is not doing much work, so it does not lose much energy, and therefore only cools down a bit. What is going on is not an isentropic expansion, but something closer to free expansion. The air still has to do some work to push the outside air out of its way, but not as much as if it was expanded gradually from the 8,000 ft cabin altitude (in which case it would get down to similar temperature as outside).
The only reason for exposure to cold would be if the cold outside air was rushing into the cabin. Which the wall between the cabin and cockpit minimized, plus the engines were still running and supplying warm air.

When air depressurizes, it does get colder, but a 0.3 bar difference wouldn't be a heck of a lot. Work around a mechanic's shop sometime - the compressor gets hot and has an intercooler, and the air vented from air tools is cold even though the air line to the air tool is room temperature or a bit warm.  Fact is, air conditioning would work even without the enthalpy of vaporization :)

@Harper-ReinstateMonica The troposphere is in thermodynamic equlibrium and that means that if you take air from one level and adiabatically expand it to a pressure at higher level, it will match the temperature at the higher level too. The cabin air is a bit warm for the 2 500 m level, but it would still cool down to -40°C to -50°C at FL360 adiabatically. Fortunately, decompression isn't adiabatic, so the air will not cool down to anywhere near that.

@Harper-ReinstateMonica, the tools in contrast do expand the air (approximately) adiabatically, because the pressure is used to drive the tools and that is what cools the air. The air-cycle machine works similarly. It takes the hot pressurized air—compression always heats the air, because the compressor must do the work and that ends up as heat in the compressed air—cools it down in the intercooler and then expands it through a turbine to make it adiabatic expansion and cool it further below the initial temperature. But decompression isn't adiabatic.

adiabatic → isentropic. Free expansion is still adiabatic, because there is still no transfer of heat; the difference is that it increases entropy.

Great question with an interesting history.
The barrier between the flight deck and the cabin of commercial aircraft is engineered to blow out in a controlled fashion upon sudden decompression like the other barriers discussed in Jan's answer.
However, after 9/11, the FAA mandated reinforced doors to prevent unauthorized access. These doors are much heavier than their predecessors, and the security requirements basically dictate that they be one single hunk of material.
Now, consider a decompression event in which the big, heavy door gets rocketed one direction or another. Bad news for anything or anyone in its path:

The pressure differential and the force on the sealed cockpit door
might be too much for the frame structure to handle if the cockpit
depressurizes first. Passive and active internal venting (dado panels)
may malfunction, get clogged by flying debris, or simply not react
fast enough to relive [sic] the pressure differential on the security door.
A loose, heavy, armored door can be much more dangerous than no
door at all (or light door), as it could seriously injure or kill the flight
crew, jam and/or destroy flight controls, damage and destroy flight
instruments, and create mayhem in the cockpit. Such a scenario is
incredibly dangerous, as it may prevent emergency descent. The rise
of pressure differential and the force across the cockpit security door
may well be much quicker than the designed venting system is
capable of handling.

A solution was needed to nearly instantaneously unlock the door when a major pressure difference was felt. Enter the decompression sensing module, some variant of which is almost universal at this point. It integrates with the other components of the flight-deck access system and can unlock the door in a small fraction of a second:

In 2001 the commercial aircraft OEMs needed a solution to rapidly unlock the cockpit door in the event of a decompression event. NAT Engineering developed an electrical solution that responded to a decompression event in the millisecond range. In a matter of months it was taken from concept, through engineering design, computer modeling, prototyping, R&D testing, formal qualification testing, and into production for delivery to the OEMs. The NAT electrical device included integration of control for the keypad, thus providing for a secure keyless entry solution.

A fun thing about the DSM is that one way to test it is by shooting it with a high-powered handgun loaded with a blank cartridge. Makes for an interesting day in the lab.

There are two different factors to consider:
First, there is the ambient air pressure - cabin and cockpit are not really separated in regard to pressure. So both would suffer from the "leak" nearly the same.
On the other hand, there are wind effects - and these are considerably stronger close to the leak, especially when in front of the airflow.

And what's going to fail first - the cockpit door, or some of the other internal structures around it / near the bulkhead - that possibly weren't hardened...

@MrR, nothing; there is enough completely open space, or space covered only by loosely fitted panels, to allow the pressure equalize without damaging anything.


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If a Cessna 172 is dropped from the sky, what minimum altitude is needed to safely land?
If an aircraft like a Cessna 172 is dropped from a helicopter, what absolute minimum altitude above the ground will be required to safely land the aircraft?

CONDITIONS:

Weather: Perfect conditions, 0 knot wind.
Ground: 0f ASL.
Gross weight: Max gross weight.
Engine: off.
Speed: 0 knot(standstill drop).
Pitch Attitude: 0 degrees(as in the picture).
The helicopter is just an "abstraction"(there is no downwash exerted on the airplane)

PS: if you can simulate this on XPlane your results will also be welcomed(I don't have it).
Also, if you want to answer from a slightly different scenario like a stall, though not the same as the scenario described above, your answer will also be welcomed.
NOTE: The question is purely about physics / aerodynamics. Not planning on doing this in real life.

Btw, you did not actually specify the pitch attitude of the airplane at the moment of release.  (You drew a picture but did not say that it was supposed to exactly constrain the situation under consideration.)   The pitch attitude of the airplane might matter a lot.   Google "hang glider balloon drop", this is a zero-airspeed situation at least as far as horizontal airspeed goes, and it has been found to be the best practice to drop the glider in a strongly nose-down pitch attitude.

@quietflyer that video was very useful to see the physics in a real life example. It looks he is at 0 degree attitude though. The recovery was very quick btw, almost instant, really surprised.

Glad I could contribute something useful -- keep in mind though that the moment of rotational inertia of a hang glider might be much lower than that of a Ces. 172--  PS you may not have watched the same video that I did, I know some of the training manuals for hang gliding recommend a rather nose-low pitch attitude for balloon drops--

watched this: https://www.youtube.com/watch?v=YB1IH2CgGB4

Not to be pedantic, but groundspeed is irrelevant.  Forward airspeed is what matters.

Does the dropped-aircraft already have a lifting point that is structural in that location, or is it added just for this test?  IE, does the hook change the flight/loading chars of the cessna ?

Does this question: Can a free-falling aircraft with no horizontal (or minimal horizontal velocity) start up and fly to safety? answer your question?

Minimum altitude is 0 ft: simply release the plane and let it sit pretty on the ground. Call it cheating, but it fits the scenario perfectly.
If you want it high in the air, what probability of landing is required? Aircraft can sometimes land in the strangest of circumstances. So let's say there's at least a 1% chance at any altitude.
If it's being dropped from an actual helicopter, rotor downwash and attitude will affect the outcome. Safe practice for stall recovery normally requires 3,000 ft, recovery itself takes less than 1,000 ft - so that's a safe altitude, but it's done in a plane with some forward airspeed.
If the "helicopter" is an abstraction, and the conditions are better, this depends on just how good the conditions are. At the right speed and attitude on the glideslope, any altitude will work.
With the new input - 0 airspeed, no engine:
A non-aerobatic GA airplane like the 172 is at risk. At zero initial airspeed, the control surfaces have zero authority; the plane might spin or tumble and never resume controlled flight. Or it might fall nose-down, but that's a gamble.
4+ generation fighters and high-end aerobatic aircraft would most likely recover. They have all-moving tails, oversized control surfaces, can take the g-loads involved, and fighters add thrust vectoring and computers.

It takes 3000ft to recover from a (power off) stall in a Cessna 172?

@tedder42 To do so safely. But I'm not sure what it takes and if it's been done from power off and zero airspeed condition.

Stalls are often done at 3000 feet, but yikes, a power off stall recovery, even without reapplying power, doesn’t take more than a couple hundred feet.

@tedder42 But that happens when you're already in controlled flight, and lost some airspeed. Your controls work. A plane dropped from a helicopter isn't going to be stable or controllable to begin with.

Not disputing that. But your original statement of “Stall recovery normally requires at least 3,000 ft.” was wildly inaccurate.

@tedder42 True. I missed the "safely" qualifier. As for the actual answer for recovery from 0 airspeed, I think the only way to figure it out is to try it in a simulator, probably X-plane. Unless someone's got a skycrane, a spare 172, and a pilot with a death wish.

Or, edit the drawing so it drops with the nose pointing down...

@Therac does something like a Extra 300 (with engine off) would be able to recover?

@Gabe No idea. You'd have to test it in a simulator. X-Plane actually has an Extra 330 module. I recommend that one because it relies almost entirely on physics-based simulation, which is more accurate in abnormal cases like this one.

A C172 dropped from standstill is more than likely recoverable. Worst case is it enters a spin, which is recoverable if C172 is within weight&balance. More likely it just goes 45+ degrees nose down almost immediately (due to tailplane generating a force), and picks up airspeed in a non-spin spiral until controls regain authority.

"The aircraft might spin or tumble and never resume controlled flight." Agree it might spin or tumble (though I think a spiral is dramatically more likely for reasons I've laid out in my answer), but why would this prevent it from resuming controlled flight? Whether it goes nose down or nose up it will regain control authority as it speeds up, and a 172 should be recoverable from any attitude so long as it has sufficient altitude and can avoid breaking up. You'd definitely want a pilot comfortable with aerobatics at the controls, though!

@Chris IDK. I just know I wouldn't risk it. A lot of good pilots have bought the farm in spins and spirals. There's a lot of uncontrolled flight modes that can happen from zero airspeed. The control surfaces don't work when the main surface is stalled, and they can break off if the wind's too strong. I believe some pilots, sometimes, will recover, but far from all.
Aerobatics or jet fighters are very different, their large all-moving surfaces work even when airflow over the wing is completely detached.

@Therac Certainly I would never suggest anyone try this maneuver in real life. But in principle it is probably safer than other stunts that are actually done in real life (which I also would never suggest anyone do in real life lol). Actually the second one is pretty similar- taking off from a helipad at very little forward speed is not so different from being dropped from a helicopter!

@Chris That's a Red Bull Carbon Cub, though! Twice the power/weight, 60 ft takeoff distance, full aerobatic build. Guess I should try it in a simulator to see how it goes, just have to set it up properly. My guess is, the heavy engine in front will save the plane most of the times, but not every time.

@Therac Yes, doing some back-of-the-envelope calculations it looks like its actually closer to its flying speed when it goes over the edge than I first imagined. So it's certainly not a 1:1 comparison.

Are we going to have a flood of questions about all the ways one might hang a c172 and whether it can recover?   Like "hung from prop" and "from wingtip" and "from rudder" and "from one undercarriage wheel" ... etc ?

"So let's say there's at least a 1% chance at any altitude." - not really. If the altitude is not enough for it to start flying, but enough to be utterly destroyed, there is zero chance. Drop it from 100 feet, and unless you prepared something below it, it will 100% be destroyed.

Not much in principle. In freefall, the 172 would reach its stall speed in a little over a hundred feet. You'd need to make sure to get the nose down as soon as possible. Then you need to gain a little more speed and pull out of the dive. Probably less than 1000 feet in total to recover to controlled flight as long as you can get the nose down relatively quickly. Then you still need however much altitude is required to find a safe landing spot. To do this remotely safely, you'd want a very healthy margin.
The plane would most likely enter a spiral at first. Both the wings and tailplane are behind the center of gravity, so unlike in normal flight they both produce a nose-down moment when they have air coming from below, and at 90 degrees angle of attack they are producing a lot of upward force along the vertical axis for a given vertical speed- significantly more than they would produce in horizontal flight at the same speed!
So the nose should drop pretty quickly even without pilot input. With the engine off, the airframe is completely symmetrical and there is no yawing or rolling moment. Eventually one wing will drop by chance and the plane will enter a spiral. But as the nose drops, the airspeed increases and the pilot regains control authority. Then they only need to recover from the ensuing dive.

"at 90 degrees angle of attack they are producing a lot of upward force along the vertical axis for a given vertical speed- significantly more than they would produce in horizontal flight at the same speed!". It's comparable. Airfoils right before stall have a lift coefficient of ~1.5 and a flat plate drag (a good approximation for the falling plane) is ~1.3. It's counter-intuitive that an airfoil with a modest downward deflection of air can produce as much lift force as a flat plate produces drag!


text:
Where is flight following available?
What local facilities are required for me to get flight following services?  It seems that if I'm 100 miles from any control tower then I won't be able to get flight following.  How close does a control tower need to be for me to be able to get flight following?  And is flight following available when only Class D towers are close by, or do I need to be close to a Class C?  Class D airspaces usually do not have approach and departure control, so I'm not sure if flight following is available when only Class D airspace is nearby (no class C).

IANAP, but I'd suggest that you book some time with your favorite flight instructor specifically to work on flight following procedures. Schedule a trip, ensure you put yourself in a position where you can get flight following (probably just about anywhere in the continental US, elsewhere YMMV). Pre-flight review your plans with the CFI(I), get in the air and get on the radio. No better way to learn it than by doing it with a competent guide by your side.

@ManuH I don't think this is a resoure location question.

In the US, you can get flight following anywhere there is radar services from ATC. It is not dependent on a control tower. However, it is dependent on ATC workload. Most controllers in our area would prefer to talk to every blip on their screen. Especially near or under their Bravo shelves.
You can pick up flight following by contacting the appropriate controlling authority/agency in controlled airspace. If you are at an airfield with a control tower, find out from them if they have radar services. Some Class D airports do have it. They will give you an abbreviated CRAFT clearance (more than likely when you contact Ground) so that Approach Control can identify you after takeoff and climb out.
If the airfield does not have a tower with radar services, you will have to climb to an altitude to be able to be seen on either Approach or Center’s radar. Cold call them on your initial call with just your tail number and the words “with request”. When/if they respond, request flight following to your destination at your desired altitude. They will let you know if their workload permits it. If they do not respond, climb higher and/or fly further into their controlling airspace (unless you have not received clearance when applicable). Or, you can try another nearby controlling agency.
Your sectional chart will tell you the information for Approach and Center. If you have difficulty locating it, look at the approach, arrival, or departure charts of any airport with instrument procedures, regardless of if they have a tower. Another alternative for getting the information is the US Cart Supplement. The controlling authority/agency information will be listed if they provide radar services to the airfield.
You can also request flight following while airborne enroute or within the terminal arrival area. Some busy airports actually require it. The information for Approach may be listed on the ATIS in this case.


text:
Other than fighters, which airplanes can fly straight up?
I would think, for example, all modern fighter jets can maintain 90 degree climbs due to having thrust to weight ratio greater than one.
Are there any other air planes which can do that?

The general answer to your (general) question is: all airplanes can do that. With every air plane you can accelerate to maximum speed pull the stick until you reach 90°.
The problem is that not all planes will be able to recover safely from that maneuver.
Most planes will not maintain enough speed to continue the flight in a controlled manor.
That's why the flight management software of modern Airliners will prevent that from happening.
On the other hand there are quite a lot planes out the able to do acrobatics like this. They have specially designed  aerodynamic behavior and, if powered,  mass/thrust ratio. The powered versions also need special engines that keep running at zero or negative G.

Are you certain that every plane has enough inertia at Vne and enough elevator authority to reach 90° before stalling? – StephenS

My claim holds, when any aircraft can reach a pitch of 90° before its speed is 0 and the pitch rate does not exceed the structural limits of the plane.
When flying strait upward gravity is slowing down the aircraft with 1G (9.81m/s²).
The time to decelerate an aircraft to 0 with 1G is=
t = v/1G

While "rotating" from horizontal flight to 90° angle this deceleration gradually raises.
Therefore real time til full stop is longer. But lets keep the calculation simple.
For a Sailplane (no thrust) like an ASK21 top Speed is 250km/h = 70m/s
t =  70m/s / 9,81m/s²
t =  7,135s

The ASK21 must be able to pitch to 90° in roughly 7 second, which is a pitch rate of 12° per second (and it is, I've done it already... ;o))
Lets recalculate for an A380:
Cruising speed 900km/h = 250 m/s
250m/s / 9.81m/s² = 25s
90° / 25s = 3,5°/s

On a quick search I could not find a resource giving the maximum pitch rate of an A380, but I'm pretty sure it is higher.
Conclusion: The faster the plane the more time is available and the less pitch rate is needed to rotate to 90°.
And yes, I keep my statement that (from a physical point of view) every aircraft can reach 90° pitch. But may not safely recover from it.

See edit. He would want to know an example of a plane with TWR above 2

Above 1 would surely be enough @Abdullah

@Sanchises typo

Are you certain that every plane has enough inertia at Vne and enough elevator authority to reach 90° before stalling?

@StephenS I did dot restrict to stall speed being the a limit, just reaching 90° pitch still moving upward potentially below stall speed. But after  the calculation in my update I'd say yes to that too (still saying that it will not maintain enough speed to recover safely).

The current version of the question has the word "maintain" in it.


text:
What is the effect of Mach number on efficiency, thrust and specific fuel consumption of a ramjet engine?
My graphs show that overall efficiency and thrust first increase, reach a peak and then fall in the supersonic range (M=1-5) whereas SFC first drops and then increases rapidly near M 5.
Why does this happen?

Welcome! A verb is missing here: "SFC first and then decreases" (increases?)

The thrust of a ramjet depends on the dynamic pressure of the airframe since this determines how high the pressure inside the ramjet can become. Thrust grows therefore initially with the square of speed.
The efficiency of heat engines depends on the temperature and pressure ratio of their cycle, and again speed helps to improve that. The specific thermodynamic process of ramjets is the Joule cycle (in the US called Brayton cycle).
Why this doesn't grow indefinitely has to do with nonlinearities at high temperature. Once gas temperatures exceed 2000 to 4000K, Oxygen starts to dissociate, depending on pressure. Nitrogen follows beyond 8000K. Now the combustion heat will not be converted into a further temperature increase but will be wasted in the dissociation of air. As this limit is approached, less margin for heating is left and the SFC drops. The optimum with current technology is at approximately Mach 2.4.
A possible remedy is to slow down the air less, so the maximum heat inside the combustion chamber can be restricted. However, the flame propagation speed of conventional hydrocarbons puts a firm and low limit to that. The higher speed simply means that mixing, evaporation and burning will happen mostly once the air-fuel mixture has left the engine. Here you need to switch to hydrogen and a supersonic ram jet, but that will bring a host of new problems.

May I mention the hilariously dangerous shcramjet.

Thrust
For a given fuel, ramjet thrust vs mach number trend may be approximately(see note 1) given by
Thrust = flight mach number(sqrt(2000 / (air temperature * (1+(7 * flight mach ^ 2) / 40))) - 1)

TSFC
If we maintain a given air/fuel ratio, the amount of fuel consumed goes up linearly with mach, as air flow rate goes up with the same trend.

Notes
Note 1: The source's equation was simplified and some values rounded off to give the current equation.

Ooops I made a big mistake. Am fixing

Fixed the issue

Do you have sources or an explanation for how you derived the formula?

@ROIMaison Will work on it.